1. Field of the Invention
The present invention relates to peristaltic pumps driven by a single speed power source and in particular to peristaltic pumps whose volumetric delivery rate is adjustable.
2. Description of the Prior Art
A peristaltic pump consists of a flexible tube within a housing having an arcuate chamber where a flexible tube is circumferentially compressed by a series of rollers or an eccentric against the wall of the inner chamber. As the rollers move along the tube, they force fluid through the tube. The displacement of fluid or the delivery rate of a peristaltic pump is determined by the flexible tubing diameter, the motor speed and any gears between the motor and the pump rollers.
In the prior art, peristaltic pumps have been in use since at least 1891. The Burson U.S. Pat. No. 460,944, issued in 1891 shows an example of a peristaltic pump of that period. A list of some of the prior art since 1891 showing the general principles of peristaltic pumps is as follows:
______________________________________ Oliveras U.S. Pat. No. 1,741,070 Santiago et al 1,988,337 Knott 2,314,281 Wittenberg 2,403,572 Bogoslowsky 2,414,355 Vogel et al 2,885,967 Simer et al 2,930,326 Daniels 2,955,543 Seyler 2,977,890 Brkich 3,067,692 Worth et al 3,358,609 Muller 3,384,080 Jess 4,155,362 ______________________________________
The flexible tubing used in peristaltic pumps is important since it is the heart of the pump and has to sustain stresses from repeated flexing and abrasion due to the repeated contact with the rollers. Under repeated flexing and abrasion the flexible tubing will fail and fracture, causing leakage. A characteristically short tubing life is perhaps the most serious drawback to using peristaltic pumps more generally, and has severely limited the range of present applications. This problem has been recognized and explored in a number of prior art patents which attempt to prolong the tubing life by redesigning the tubing.
______________________________________ Seyler U.S. Pat. No. 2,693,766 Mascaro 2,917,002 Mascaro 2,925,045 Murray 2,987,004 Vadot 3,192,863 Fitter 3,875,970 Gerritsen 3,887,306 LeGeay, nee Lechat et al 4,080,113 Gerritsen 4,110,061 ______________________________________
Peristaltic pumps have an economic advantage over other types of pumps and the added cost of specifically designed tubing would take away some of this advantage. Further, the tubing of the prior art will eventually fail and need to be replaced. The risk of failure, cost of down time and the replacement cost of the prior art specially designed tubing will detract from the economic advantage that peristaltic pumps have over other pumps.
Another approach in lengthening the life of the flexible tubing is to use a buffer material between the flexible tubing and the rollers. The Stanber U.S. Pat. No. 3,583,838 shows a flexible ring 17 in FIG. 2 that seals the roller bearing of the eccentric roller of the pump. The ring 17, however, does not actually act as a buffer but acts with the roller in contacting the tubing as described previously. The abrupt and highly localized longitudinal stresses resulting in the tubing's wall generally caused by direct roller contact are not avoided. The Shlisky U.S. Pat. No. 3,591,319 teaches a conduit protective member between a plurality of rollers and the flexible tubing. However, in order for the conduit protective member to act as a buffer, the flexible conduit is stretched over the rollers sufficiently for occlusion to take place and for the flexible conduit to lie against the protective member in such frictional engagement so as to prevent wandering and eliminate any longitudinal stretching and abrasion of the flexible conduit. As a result of tightly extending the flexible conduit over the rollers, other stresses are introduced that offset any gain obtained by the protective member. The Gelfand U.S. Pat. No. 3,723,030 shows a plurality of tubes, each protected from the rollers by a nylon strip. This protective strip offers minimal protection to the tubing since it merely eliminates the contact with the roller and does not reduce the severity of the stress caused by the rollers.
Further, all the protective strips in the prior art are susceptible to abrasive wear, creep, and eventual failure from the constant action of the rollers. The failure of the protective strips results in either direct contact between the rollers and the flexible conduit or in creating the situation where the protective strip now fractured from fatigue becomes a source of abrasion. There is a need for a better protective strip for extending the life of the flexible tubing.
In order to change the delivery rate of the peristaltic pumps of the prior art, the diameter of the flexible conduit was changed as taught in the Gelfand patent. Changing the flexible conduit requires stopping the pump and substituting a different size conduit to change the delivery rate. The delivery rate could also be changed by varying the rotor speed, as is also taught in the Gelfand patent. The Berman et al U.S. Pat. No. 3,737,251 and Vial U.S. Pat. No. 3,990,444 show stepping motors being used to vary the rotor shaft speed. Stepping motors and other variable speed motors are expensive and eliminate the economic advantage that peristaltic pumps have over other pumps. Pumps such as piston pumps can easily change their delivery rate by merely varying the stroke of the piston. There is a need for a peristaltic pump having the capability of a variable delivery rate without the use of an expensive variable speed motor or the need of shutting down the pump and changing the flexible tubing.